In high-power field examination, which finding is most consistent with a fiber artifact rather than a true cast?

• A. Granular cast
• B. Hyaline cast
• C. Waxy cast
• D. Fiber artifact

Answer: (D)

When evaluating urine sediment under high power, recognizing artifacts versus true casts is essential. A true cast forms in the renal tubules and has a definite cylindrical shape with a consistent protein matrix; its outline and internal texture reflect its tubular origin. A fiber artifact, however, is a contaminant that looks like a filament rather than a genuine cast. It appears as a slender, thread-like structure—sometimes with frayed or irregular ends—that does not conform to the smooth, uniform cylindrical contour or layered matrix of a cast. Because it lacks the tubular architecture of hyaline, granular, or waxy casts, a fiber artifact is the finding most consistent with an artifact rather than a true cast. In practice, if you see a long, filamentous piece that doesn’t resemble cast morphology across multiple fields, it’s more likely a fiber artifact.